This invention relates to a photosensitive compound useful as a photosensitive agent for lithography, e.g. for producing semiconductor devices.
With recent higher density and larger scale integration of semiconductor devices, wavelengths used in exposing devices for minute processing, particularly for lithography become shorter and shorter. Now, KrF excimer laser light (248.4 nm) is studied. But, there have been no photosensitive materials suitable for such a wavelength.
For example, even when MP 2400 (mfd. by Shipley Corp.), which is known among photoresists to have high sensitivity to KrF excimer laser light and good light transmittance, is used, pattern formation after development is very bad and cannot be used practically [K. Ogawa et al., J. Electrochem. Soc., 135, p2347 (1988)].
This seems to be derived from the fact that MP 2400 resist has a large surface absorption for the exposed light.
This can be interpreted that the main polymer (resin) per se used in the resist has a large light absorption against the exposed light, or a photosensitive material in the resist has no good light reactivity. That is, photosensitive materials such as naphthoquinone diazides heretofore used in known resists generally have a large absorption against a light near 248.4 nm and are hardly improved in transmittance after exposure to light. For example, in the case of MP 2400 with a film thickness of 1 .mu.m, changes in light transmittance before and after exposure to light of KrF excimer laser (248.4 nm) is only about 3% at 248.4 nm as shown in FIG. 3 wherein the full line is before exposure and the dotted line is after exposure. This means that the reactivity is poor.
On the other hand, U.S. Pat. No. 4,622,283 to Gray discloses a lithographic resist composition for use with deep UV light of less than 300 nm wavelength containing as a photosensitive solubilizing agent a compound of the formula: ##STR3## wherein R.sup.1 and R.sup.2 can each individually be alkyl, aryl, alkoxyalkyl, aralkyl or haloalkyl radicals or R.sup.1 and R.sup.2 taken together can be an alkylene radical. But this composition is insufficient in preventing non-light exposed portion from erosion of an alkaline developing solution to cause erosion of retaining portions of resist film (hereinafter referred to as "film erosion") in large amounts, which results in causing deterioration in contrast of the resist pattern.
Further, U.S. Pat. No. 4,339,522 to Balanso et al disclose a lithographic resist composition comprising a phenolic-aldehyde resin and a deep ultraviolet sensitizer of the formula: ##STR4## wherein R.sub.1 is alkyl or aryl; and R.sub.2 is H, alkyl or aryl, or together R.sub.1 and R.sub.2 are cycloalkyl. But this U.S. Patent is quite silent on the reactivity against KrF excimer laser, resistance to alkaline developing solution and improvement in the contrast.